linux-kernel - Re: [PATCH]tickless: Fix tick nohz timer irq0 fail to increaase

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Date:	Mon, 04 Jan 2010 15:00:49 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	"Youquan,Song" <youquan.song@...ux.intel.com>, hpa@...or.com,
	tglx@...utronix.de, akpm@...ux-foundation.org,
	venkatesh.pallipadi@...el.com, suresh.b.siddha@...el.com,
	kent.liu@...el.com, chaohong.guo@...el.com, youquan.song@...el.com,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	"jens.axboe" <jens.axboe@...cle.com>
Subject: Re: [PATCH]tickless: Fix tick nohz timer irq0 fail to increaase

On Mon, 2010-01-04 at 04:36 -0800, Arjan van de Ven wrote:
> > cause is that it is default to enable high resolution timer which
> > will force to oneshot broadcast mode.
> 
> using local apic in one shot mode is not a problem, I'd in fact call it
> a feature... 

lapic yes, broadcast not so much.

He mentioned he was using Nehelem-EX which is known broken in that it
stops the lapic in deeper C states and thus reverts to HPET broadcast
since there's not enough HPET timers to go around.

Something like processor.max_cstate=2 should fix that IIRC.

Jens ran into this on his shiny new box.

Disabling nohz is funny indeed, one wonders why he does that.

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